1. Field of the Invention
This invention relates generally to a method and apparatus for lifting objects, and more particularly, for a method for rolling a vacuum lifter off an object.
2. Description of the Related Art
FIG. 1 illustrates a prior art vacuum lifter 10 for lifting and transporting an object 12. The object 12 may take any form as long as at least one surface 14 is smooth and firmly fixed to the object 12. The vacuum lifter 10 includes an overhead vacuum hose 16 that is airtight. The overhead hose 16 has a substantially vertical portion terminating in a first end hermetically connected to the intake of a vacuum pump (not shown). A second end of the overhead hose 16 hermetically connects to a metal housing 18. The hose 16 is supported by an overhead structure (not shown) that supports the weight of both the lifter 10 and, when lifted, the object 12. In some cases, the overhead structure includes rollers and tracks (not shown) that facilitate horizontal displacements of the loaded lifter 10.
The housing 18 has airtight internal passages (not shown) that connect the overhead hose 16 to one or more secondary hoses 20. The housing 18 also has a support structure 22 fixedly connecting one or more sealing plates 24 to the bottom thereof. Each secondary hose 20 hermetically connects to an upper surface of the sealing plate 24 and connects with a lower surface thereof through one or more holes 26 that pierce the sealing plate. A pliable sealing ring 30 attaches to the entire perimeter of the lower surface of each sealing plate 24. The sealing ring 30 hermetically seals the lower surface of the sealing plate 24 to the top surface 14 of the object 12 upon compression therebetween.
One or more handles 28 project from the housing 18. A control lever 32 projecting from the housing 18 operates internal valves (not shown) regulate the vacuum pressure in the secondary hoses 20. The vacuum lifter 10 forms a sealed conduit between the intake of the vacuum pump (not shown) and the surface 14 of the object 12 when a vacuum is created therein.
FIG. 2A illustrates the operation of the vacuum lifter 10. The vacuum lifter 10 is positioned so that the sealing plate 24 is snug against the smooth surface 14 of the object 12. A vacuum is produced between the surface 14 and the sealing plates 24 by means of the secondary hoses 20. The vacuum forms a suction that grips the object 12 to the lifter 10. Since the conduit formed by the overhead hose 16 between the sealing plates 24 and the vacuum pump (not shown) is hermetically sealed, the vertical portion of the overhead hose 16 is flexible and shortens as the vacuum therein is increased.
As the vertical portion of the overhead hose 16 shortens, the object 12 is lifted off the ground 34. An operator 36 may adjust the height of the object with the control lever 32 that regulates the vacuum in the overhead hose 16 and the length thereof by allowing air to enter through valves (not shown) connected to the outside. After the object 12 is positioned at the desired height, the operator 36 moves the vacuum lifter 10 and the attached object 12 by pushing or pulling with the handles 28 or by pushing or pulling on the object 12 itself.
FIG. 2B illustrates the removal of the vacuum lifter 10 from the object 12 after the object 12 is positioned on the desired surface 38. The operator 36 allows air to enter the secondary hoses 20 to release the vacuum between the sealing plates 24 and the surface 14. The object 12 is consequently released from the vacuum lifter 10. After the vacuum is released, the operator 14 attempts to slide the vacuum lifter 10 off without disturbing the positioning of the object 12.
Since the vacuum lifter 10 is heavy, the operator 36 may have difficulty in sliding the lifter 10 both on and off the object 12 to be lifted. Sliding the vacuum lifter 10 on or off is specially difficult when the object 12 has been placed on a surface above the shoulders of the operator 36. Since the vacuum lifter 10 cannot be easily slid on or off objects 12 positioned at shoulder height, the lifter 10 is less useful as a warehouse tool.
Some vacuum lifters 10 allow reversing the air flow in the secondary hoses 20. After the air flow is reversed, the lifter 10 rests on a cushion of air between the sealing plates 24 and the surface 14 of the object 12. The cushion of air facilitates sliding the vacuum lifter 10 on or off the object 12. Unfortunately, reversing the air flow in the vacuum lifter 10 requires relatively substantial time because the overhead hose 16 is wide and must generally be refilled with air. For such prior art lifters 10, the operator 36 may have to wait thirty seconds for the vacuum pump to form a sufficient air cushion. In some other lifters 10, a reversal of the airflow is inconvenient because reversing the airflow eliminates the lifting force exerted by the overhead hose 16. These construction and time delay constraints compromise the usefulness of reversal of the internal airflow as an aid to sliding the lifter 10 on or off an object.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.